1. Field of Invention
The invention relates to a display apparatus and, in particular, to an organic light-emitting diode (OLED) display apparatus.
2. Related Art
Recently, the OLED with various advantages, such as high brightness, full color, wide viewing angle, self-emission, fast response speed, flexibility, simple manufacturing process, low cost, etc., is developed. Compared with the liquid crystal display technology, the OLED display apparatus is a better choice with considering the property requirements of flat display apparatuses.
FIG. 1 is a schematic diagram showing the pixel circuit 10 in a conventional OLED display apparatus. As shown in FIG. 1, the pixel circuit 10 comprises a scan line S and a data line D crossed in the form of a matrix, an n-type thin-film transistor 11, a p-type thin-film transistor 12, a capacitor 13, and an OLED 14. The gate of the n-type thin-film transistor 11 is connected with the scan line S, the drain thereof is connected with the data line D, and the source thereof is connected with the p-type thin-film transistor 12 and the capacitor 13. Accordingly, within a frame time, when the scan line S outputs a scan signal to turn on the n-type thin-film transistor 11, the image data is inputted to the capacitor 13 through the data line D and the n-type thin-film transistor 11. At this moment, the p-type thin-film transistor 12 is turned off. After that, the n-type thin-film transistor 11 is then turned off, so that the p-type thin-film transistor 12 can be turned on according to the image data stored in the capacitor 13. Consequently, the power source Vdd can be inputted to drive the OLED 14 to emit light.
The memory 15 stores pixel data which should be written into pixel circuit 10. The gate driver 16 control the pixel circuit 10 to receive image data from the source driver 17, and thus the source driver 17 writes the image data stored in the memory 15 into the pixel circuit 10.
Regarding to the resolution of QVGA, there are totally 320 pixels connected with the data line D, and the analog voltage corresponding to the image data is transmitted to the pixels in order through the data line D. Before next frame time, each pixel must maintain its brightness corresponding to the inputted analog voltage level. Since the brightness of each pixel is a function of the gate voltage of the p-type thin film transistor 12, the gate voltage of the p-type thin film transistor 12 should be remained for the period of a frame time (about 16.6 msec) by the capacitor 13.
However, the leakage current issue may occur in both the n-type thin-film transistor 11 and the p-type thin-film transistor 12, which will consume the electricity stored in the capacitor 13. Thus, the voltage level of the image data stored in the capacitor 13 may be changed. After a long period (e.g. longer than a frame time), the gate voltage of the p-type thin film transistor 12 is not guaranteed. This also leads to that the p-type thin-film transistor 12 can not be turned on or off according to the correct image data during a frame time unless new image data is provided. Nevertheless, the power consumption of the display apparatus is increased.